1. Field of the Invention
The present invention relates to novel stainless steel type 13Cr5Ni, and the usage of the same in fluid machinery such as hydraulic turbine runners and guide vanes, which are assembled into a hydraulic turbine generator or a pumped-storage hydraulic turbine generator, and impeller for a pump, and fluid machinery made of 13Cr containing Ni martensitic stainless steel which has previously been cladded by welding with welding material having corrosion resistance and welding crack resistance at portions of the machine where cavitation erosion is anticipated.
2. Description of the Prior Art
As JP-B-42-16870 (1967) disclosed, stainless steel type 13Cr5Ni contains approximately 30% austenite in a martensitic matrix, accordingly, stainless steel type 13Cr5Ni has both the large strength of martensitic steel and the high toughness of austenitic steel. Stainless steel type 13Cr5Ni has significantly better weldability than 13Cr steel which does not contain Nickel. However, the welded portions without any annealing treatment have a ductility and toughness lower than the base materials because of hardening of the heat affected zone.
For fluid machinery, material having a large strength and a high toughness is required in order to restrict the cross sectional area of machines to increase fluid flow rate and efficiency. Stainless steel having preferable toughness were disclosed in JP-A-60-63357 (1985) and JP-A-60-174859(1985).
Hydraulic turbine machines exposed to high speed rotation and rapid fluid flow in fresh water and sea water generate cavitation at local portions which would cause vibration and noise, and decrease efficiency. Further, the surface of the local portions would be damaged by cavitation erosion. Therefore, the use of 13Cr cast steel containing nickel having more preferable erosion resistance and desirable strength characteristics than conventional material is becoming widespread as a material for runners of hydraulic turbines which are large scale apparatus. However, the hydraulic turbine machine is still damaged by erosion depending on the scale or operating condition such as speed of rotation, and consequently, the development of a repairing technique is desired.
Generally, an erosion resistant welding material for suppressing the above damage, a cobalt base alloy, called stellite, containing Cr, Ni, Mo, and others which are standardized in JIS:Z3251 and AWS:A5.13, is well known. However, the above welding material is expensive because it includes a large amount of cobalt, and further, its cladding layer has a high carbon content (0.90-3.00%) and a high hardness (Vickers hardness; 400-550). Accordingly, when the cladding area is broad, weld crack sensitivity increases and workability at the surface of the cladding layer becomes difficult. Therefore, because of the weld crack sensitivity, pre-heat treatment and post-heat treatment at a high temperature (550.degree.-650.degree. C.) is applied to the cladding layer even if an intermediate cladding layer of austenitic welding material is provided at the surface of the base material.
Accordingly, there are many problems in assuring the safety of workers when performing welding repairs in a narrow place on a machine, and many issues concerning workability and lowering cost remain.
Therefore, because of the above reasons, austenitic welding material such as D(E)-308, D(E)-309, D(E)-309Mo which are standardized in JIS: Z3251 and AWS: A5.4 are mainly used in welding repairs of parts of such hydraulic turbines, because, although the above material is inferior in erosion resistance to the cobalt base alloy group welding material, the material has a low pre-heating temperature, preferable weld crack resistance, and a relatively low price. JP-B-42-24813 (1967), JP-A-58-37162 (1983), and JP-B-62-54863 (1987) disclose such cladding weld materials.
However, the above conventional welding repair materials have many issues to be solved such as the incapability of realizing sufficient resistance against damage to fluid machines by cavitation and soil under severe operating conditions such as with large scale machines and increasing speeds of rotation. Further, usage in corrosive environments such as sea water is desired, and accordingly, development of materials which resist erosion in addition to corrosion and abrasion is required.
Therefore, surface treating weld cladding materials for suppressing damage of the composing parts of fluid machinery such as hydraulic turbines by cavitation and soil as described above, having better resistance against both erosion and corrosion, and superior weldability are desirable.